1. Technical Field
The present disclosure relates to an image reading device and an image reading system for reading images containing a portion printed with ink that reflects visible light when exposed to ultraviolet light.
2. Related Art
When a check is presented to a financial institution, the check is read by a check processing device, magnetic ink characters printed on the check are magnetically read, and payment is processed based on the acquired magnetic information. Parallel to reading the magnetic ink characters, the check processing device also emits visible light to the front of the check to capture an image of the check, and the financial institution stores the acquired check image as proof of the transaction. When a check bearing an image printed with ink (UV ink) that reflects visible light (fluoresces) when exposed to UV light to prevent forgery is presented to a financial institution, the check processing device reads the front of the check with UV light by exposing it to UV light, and uses the acquired check image to determine the authenticity of the check.
One example of a check processing device that can be used in such check payment processes is described in JP-A-2013-70225. The check processing device described in JP-A-2013-70225 has a magnetic sensor for magnetically reading magnetic ink characters, and an image sensor for optically scanning the check face to capture an image of the check. This check processing device conveys checks through a conveyance path past the magnetic reading position of the magnetic sensor and the scanning position of the image sensor, reads the magnetic ink characters with the magnetic reader, and images the check face with the image sensor. The image sensor emits both visible light and UV light for scanning.
In a device having an image sensor, individual differences in imaging elements and individual differences in photoemitters that emit the scanning light may result in deviation between devices in the hue and tone of the images acquired from the medium. With such devices, therefore, calibration before factory shipping is required to correct the hue and tone of the scanned images, and the scanning data output from the image sensor is corrected based on the correction value set by the calibration process to acquire an image based on the corrected scanning data. A method of calibrating an image forming device is described in JP-A-2010-263345.
The check processing device described in JP-A-2013-70225 uses two scanning methods to acquire a first image of the check by emitting visible light and a second image of the check by emitting UV light. In the first acquisition method, both the first image and the second image are captured while the check travels once through the conveyance path.
In the first acquisition method, the surface of the check is sequentially exposed to visible light and then UV light as the check is conveyed the distance of one line corresponding to the scanning resolution of the image reading device, and the one-line portion of the check exposed to visible light and the one-line portion of the check exposed to UV light are sequentially acquired to capture the first image and the second image.
In the second acquisition method, the check is conveyed twice through the conveyance path. In this second acquisition method, the check is exposed to visible light and the first image is captured while the check passes the scanning position on the first pass, and the check is exposed to UV light and the second image is captured while the check passes the scanning position on the second pass.
If the correction value is set by calibration when scanning the surface of the check by emitting UV light, it should be possible to acquire the same image whether the second image is acquired by the first acquisition method or the second image is acquired by the second acquisition method. However, the color tone (brightness, illuminance) can differ between the second image acquired by the first acquisition method and the second image acquired by the second acquisition method, and identical images cannot be acquired.
Why identical images cannot be acquired by these two acquisition methods is not clear. One conceivable reason is that the amount of light from the light source that emits the UV light is less when sequentially switching from visible light to UV light in the first acquisition method than when the UV light is emitted by the second acquisition method. Remnants of the visible light that is emitted before the UV light is emitted are another possible reason.